Damping for user defined spectrum
Posted: 17 Jul 2014, 19:42
Dear Earthquake Experts,
I am currently dealing with Indian Standard on earthquake (IS1893). In this standard default response spectrum is given for 5% damping ratio and additionally multiplication factors are given to correct the response spectrum for other damping ratios. In my case I was supposed to use the lower damping values in the range of 0.2 to 2% which gives the multiplication factors in the range of 2.6 to 1.4 for the respective damping values. By applying these multiplication factors the response spectrums were exaggerated with higher accelerations. My next step was to use SeismoArtif to generate the artificial timeseries using these response spectrums. I chose the option of user defined response spectrum and as a result I had an additional input field 'Damping' to specify the damping (%) in 'Accelogram Generation' window. In this window I got a bit confused as giving a lower damping value as input here I got timeseries matching to response spectrum with lower PGA (and also other quantities lower such as PGV, PGD, AI, Cum. abs. velocity etc). I increased the damping (%) and the PGA was increased in order to match the same response spectra. Actually I had expected the result other way round that with lower damping the ground acceleration timeseries shall be more strong and with higher damping less strong but which was not the case here.
I further used these timeseries in our aeroelastic structural loads simulation tool for large wind turbines. Normally, I had expected higher structural loads with lower damping timeseries but that was not the case as the SeismoArtif generated timeseries was already a bit softer as explained above. Could you please give some guidance about use of Damping field in SeismoArtif in case the user uploads his custom response spectrum in order to generate artificial timeseries?
I have a second related question as well:
For artificial timeseries generation I preferred to use following default settings and generated the same successfully:
Smallest period of desired response spectrum: 0.02s
Largest period of desired response spectrum: 4.0s
Time-step: 0.01 sec
Now as a next step when I want to use the artificial generated accelograms in our aeroelastic structural loads simulation tool as input what time-step should I preferably use for my load simulation tool? Same like accelogram (i.e., 0.01s) or smaller or larger and by what factor larger or smaller. Normally for your information our interesting frequency range for different vibration modes in large wind turbine are roughly 0.25Hz to 10Hz (or say maximum upto 20Hz). Considering the same is it already appropriate to use default settings of 0.02 and 4.0s for smallest and largest periods of desired response spectrum or the range could also be curtailed?
Thank you very much to all experts for providing your insights on these topics.
I am currently dealing with Indian Standard on earthquake (IS1893). In this standard default response spectrum is given for 5% damping ratio and additionally multiplication factors are given to correct the response spectrum for other damping ratios. In my case I was supposed to use the lower damping values in the range of 0.2 to 2% which gives the multiplication factors in the range of 2.6 to 1.4 for the respective damping values. By applying these multiplication factors the response spectrums were exaggerated with higher accelerations. My next step was to use SeismoArtif to generate the artificial timeseries using these response spectrums. I chose the option of user defined response spectrum and as a result I had an additional input field 'Damping' to specify the damping (%) in 'Accelogram Generation' window. In this window I got a bit confused as giving a lower damping value as input here I got timeseries matching to response spectrum with lower PGA (and also other quantities lower such as PGV, PGD, AI, Cum. abs. velocity etc). I increased the damping (%) and the PGA was increased in order to match the same response spectra. Actually I had expected the result other way round that with lower damping the ground acceleration timeseries shall be more strong and with higher damping less strong but which was not the case here.
I further used these timeseries in our aeroelastic structural loads simulation tool for large wind turbines. Normally, I had expected higher structural loads with lower damping timeseries but that was not the case as the SeismoArtif generated timeseries was already a bit softer as explained above. Could you please give some guidance about use of Damping field in SeismoArtif in case the user uploads his custom response spectrum in order to generate artificial timeseries?
I have a second related question as well:
For artificial timeseries generation I preferred to use following default settings and generated the same successfully:
Smallest period of desired response spectrum: 0.02s
Largest period of desired response spectrum: 4.0s
Time-step: 0.01 sec
Now as a next step when I want to use the artificial generated accelograms in our aeroelastic structural loads simulation tool as input what time-step should I preferably use for my load simulation tool? Same like accelogram (i.e., 0.01s) or smaller or larger and by what factor larger or smaller. Normally for your information our interesting frequency range for different vibration modes in large wind turbine are roughly 0.25Hz to 10Hz (or say maximum upto 20Hz). Considering the same is it already appropriate to use default settings of 0.02 and 4.0s for smallest and largest periods of desired response spectrum or the range could also be curtailed?
Thank you very much to all experts for providing your insights on these topics.